Of note, this color change is sensitive to even super low levels of radiation that are just considered part of modern life – like cigarette smoke and car exhaust. That said, it is a useful monitor because it grows in many climates and shows exposure within just a few days.
Spiderworts (genus Tradescantia) are a family of often ground-crawling plants found throughout North America. Though many of the species are highly invasive while others are common house plants, a handful of lab-grown spiderworts are known for something else far more unusual: they change colors in the presence of radiation.
Filament hairs are small hairs that grow from the plant’s filament – which is the stalk that holds up the pollen. Ordinarily the filament hairs of spiderworts are either blue or pink. If a spiderwort has one copy of the blue gene and one of the pink gene, the hairs will be blue.
When exposed to radiation, the DNA gets damaged and breaks. In an attempt to repair the genes, the cells may copy the segments from other DNA strands. When this break affects the color gene, the blue copy can sometimes be edited out or irreparably mutated, leaving the pink copy present. The cell and its progeny will then be pink.
There are 6 filaments in each flower, each having many filament hairs. Since this change affects individual cells, the filaments will not all suddenly turn pink – but the more radiation the plant is exposed to, the more cells turn pink. The amount of radiation present can be calculated by the proportion of blue to pink cells.